// In production, we register a service worker to serve assets from local cache.

// This lets the app load faster on subsequent visits in production, and gives
// it offline capabilities. However, it also means that developers (and users)
// will only see deployed updates on the "N+1" visit to a page, since previously
// cached resources are updated in the background.

// To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
// This link also includes instructions on opting out of this behavior.

const isLocalhost = Boolean(
    window.location.hostname === 'localhost' ||
    // [::1] is the IPv6 localhost address.
    window.location.hostname === '[::1]' ||
    // 127.0.0.1/8 is considered localhost for IPv4.
    window.location.hostname.match(
        /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/,
    ),
);

export default function register() {
    if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
        // The URL constructor is available in all browsers that support SW.
        const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
        if (publicUrl.origin !== window.location.origin) {
            // Our service worker won't work if PUBLIC_URL is on a different origin
            // from what our page is served on. This might happen if a CDN is used to
            // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
            return;
        }

        window.addEventListener('load', () => {
            const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;

            if (isLocalhost) {
                // This is running on localhost. Lets check if a service worker still exists or not.
                checkValidServiceWorker(swUrl);

                // Add some additional logging to localhost, pointing developers to the
                // service worker/PWA documentation.
                navigator.serviceWorker.ready.then(() => {
                    console.log(
                        'This web app is being served cache-first by a service ' +
                        'worker. To learn more, visit https://goo.gl/SC7cgQ',
                    );
                });
            } else {
                // Is not local host. Just register service worker
                registerValidSW(swUrl);
            }
        });
    }
}

function registerValidSW(swUrl) {
    navigator.serviceWorker.register(swUrl).then(registration => {
        registration.onupdatefound = () => {
            const installingWorker = registration.installing;
            installingWorker.onstatechange = () => {
                if (installingWorker.state === 'installed') {
                    if (navigator.serviceWorker.controller) {
                        // At this point, the old content will have been purged and
                        // the fresh content will have been added to the cache.
                        // It's the perfect time to display a "New content is
                        // available; please refresh." message in your web app.
                        console.log('New content is available; please refresh.');
                    } else {
                        // At this point, everything has been precached.
                        // It's the perfect time to display a
                        // "Content is cached for offline use." message.
                        console.log('Content is cached for offline use.');
                    }
                }
            };
        };
    }).catch(error => {
        console.error('Error during service worker registration:', error);
    });
}

function checkValidServiceWorker(swUrl) {
    // Check if the service worker can be found. If it can't reload the page.
    fetch(swUrl).then(response => {
        // Ensure service worker exists, and that we really are getting a JS file.
        if (
            response.status === 404 ||
            response.headers.get('content-type').indexOf('javascript') === -1
        ) {
            // No service worker found. Probably a different app. Reload the page.
            navigator.serviceWorker.ready.then(registration => {
                registration.unregister().then(() => {
                    window.location.reload();
                });
            });
        } else {
            // Service worker found. Proceed as normal.
            registerValidSW(swUrl);
        }
    }).catch(() => {
        console.log(
            'No internet connection found. App is running in offline mode.',
        );
    });
}

export function unregister() {
    if ('serviceWorker' in navigator) {
        navigator.serviceWorker.ready.then(registration => {
            registration.unregister();
        });
    }
}
